Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. Freon group of refrigerants are

Nontoxic and non-inflammable

Non-inflammable and toxic

Toxic

Inflammable

2. In a lithium bromide absorption refrigeration system

Ammonia is used as a refrigerant and lithium bromide as an absorbent

Lithium bromide is used as a refrigerant and water as an absorbent

None of these

Water is used as a refrigerant and lithium bromide as an absorbent

3. A bootstrap air cooling system has

One heat exchanger

Four heat exchangers

Three heat exchangers

Two heat exchangers

4. The boiling point of ammonia is

-77.7°C

-33.3°C

-10.5°C

-30°C

5. Rating of a domestic refrigerator is of the order of

40 tons

5 tons

10 tons

0.1 ton

6. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

7. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Sub-cooling or under-cooling

None of these

Super-cooling

Normal cooling

8. The freezing point of sulphur dioxide is

-75.2°C

-135.8°C

-77.7°C

-56.6°C

9. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Unpredictable

Less

Equally

10. Critical temperature is the temperature above which

Water will never evaporate

A gas will immediately liquefy

Water will evaporate

A gas will never liquefy

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11. Which of the following statement is correct?

(D) Both (A) and (B)

(B) The increase in air movement increases the evaporation from the human body.

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

12. The operating pressure for refrigerating units using R-12 as a refrigerant is

30 bar

2 bar

8 bar

15 bar

13. A thermostatic expansion valve in a refrigeration system

Maintains different temperatures in evaporator in proportion to load

None of the above

Is suitable only for constant load systems

Ensures the evaporator completely filled with refrigerant of the load

14. Highest temperature encountered in refrigeration cycle should be

Above critical temperature

At critical Temperature

Much below critical temperature

Near critical temperature of refrigerant

15. The domestic refrigerator uses following type of compressor

Miniature sealed unit

Piston type reciprocating

Centrifugal

Axial

16. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Brine

Ammonia

Freon

Carbon dioxide

17. For obtaining high COP, the pressure range of compressor should be

Low

Optimum

Any value

High

18. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant pressure

Takes place at constant temperature

Involves no change in volume

Takes place at constant entropy

19. The value of C.O.P in vapour compression cycle is usually

Any one of the above

Always more than unity

Always less than unity

Equal to unity

20. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Collect liquid refrigerant and prevent it from going to compressor

Superheat the vapour

Collect vapours

Detect liquid in vapour

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21. The curved lines on a psychrometric chart indicates

Relative humidity

Dry bulb temperature

Wet bulb temperature

Dew point temperature

22. The condition of refrigerant after passing through the condenser in a vapour compression system is

Saturated liquid

Wet vapour

Superheated vapour

Dry saturated vapour

23. The minimum temperature to which water can be cooled in a cooling tower is

Dry bulb temperature of air

Wet bulb temperature of air

Dew point temperature of air

Ambient air temperature

24. The vapour compression refrigerator employs the following cycle

Reversed Carnot

Reversed Rankine

Rankine

Carnot

25. The capillary tube, as an expansion device, is used in

Water coolers

Domestic refrigerators

Room air conditioners

All of these

26. In a refrigeration system, heat absorbed in comparison to heat rejected is

Same

Less

More for small capacity and less for high capacity

27. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

1.2

0.2

28. In a refrigeration system, the expansion device is connected between the

Receiver and evaporator

Evaporator and compressor

Compressor and condenser

Condenser and receiver

29. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

T₂/ (T₂ - T₁)

(T₁ - T₂)/T₁

T₁ / (T₂ - T₁)

(T₂ - T₁)/T₁

30. Which of the following cycles uses air as the refrigerant?

Bell Coleman

Ericson

Stirling

Carnot

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31. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

None of these

Positive

Negative

Zero

32. Cooling water is required for following equipment in ammonia absorption plant

Condenser, absorber and separator (rectifier)

Evaporator

Condenser

Absorber

33. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.4

0.67

0.376

0.6

34. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

4.33

2.33

1.33

3.33

35. Which of the following is not a desirable property of a refrigerant?

Good electrical conductor

Large latent heat

Low boiling point

High risibility with oil

36. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 9

9: 1

1: 3

1: 1

37. Most thermostatic expansion valves are set for a superheat of

15°C

10°C

5°C

20°C

38. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(B) Heat stored in the human body

(D) Difference of (A) and (B)

(A) Heat dissipated to the surroundings

39. The bank of tubes at the back of domestic refrigerator is

Refrigerant cooling tubes

Condenser tubes

Capillary tubes

Evaporator tubes

40. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

5.12

1.25

2.15

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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